Power absorbing coaxial termination comprising slab line structure with plane outer plates having inwardly curved end portions



May 18, 1965 G. R. TAHARA 3,184,592

POWER ABSORBING COAXIAL TERMINATION COMPRISING SLAB LINE STRUCTURE WITHPLANE OUTER PLATES HAVING INWARDLY CURVED END PORTIONS Filed July 2,1962 4 Sheets-Sheet 1 40 r Q0- w r GORO R. TAH

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RNEY May 18, 1965 G. R. TAHARA 3,184,692

POWER ABSORBING COAXIAL TERMINATION ,COMPRISING SLAB LINE STRUCTURE WITHPLANE OUTER PLATES HAVING INWARDLY CURVED END PORTIONS Filed July 2,1962 4 Sheets-Sheet 2 GORO R. TAHARA INVENTOR.

ATTORNE May 18, 1965 G. R. TAHARA 3,184,692

. POWER ABSORBING COAX-IAL TERMINATION COMPRISING SLAB LINE STRUCTUREWITH PLANE OUTER PLATES HAVING INWARDLY CURVED END PORTIONS Filed July2, 1962 -4 Sheets-Sheet z 00 I0 i f0 o O GORO R. TAHARA INVENTOR 3 BY AQXM ATTORNEY May 18, 1965 R, TAHARA 3,184,62

POWER ABSORBING COAXIAL TERMINATION COMPRISING SLAB LINE STRUCTURE WITHPLANE OUTER PLATES HAVING INWARDLY CUHVED END PORTIONS 4 Sheets-Sheet 4Filed July 2, 1962 GORO R. TAHARA INVENTOR.

United States Patent 3,184,692 POWER ABSORBING COAXIAL TERMINATHONCOMPRISING SLAB LINE STRUCTURE WITH PLANE OUTER PLATES HAVING INWARDLYCURVED END PORTIONS Goro R. Tahara, Sunnyvale, alif., assignor to PhilcoCorporation, Philadelphia, Pa., a corporation of Delaware Filed July 2,1962, Ser. No. 206,598 3 Claims. (Cl. 333-22) This invention relates toa coaxial transmission line termination and more particularly to a powerabsorbing load for the termination of high frequency coaxialtransmission lines.

High frequency energy is often dissipated in a load to prevent radiationof the energy, the radiant energy being converted to heat energy in theload. Often the load includes an inner conductor comprising an elongatedresistor and an outer conductor structure comprising a tapered sleevesurrounding the resistor and connected thereto at one end thereof. Thetaper of the outer conductor is preferably exponential so that thedevice exhibits a pure ohmic characteristic. Cooling of such loads isdifiicult due to the fact that heat producing resistor is surrounded bythe outer conductor structure. Numerous schemes have been proposed forcooling such loads, which schemes generally increase in size andcomplexity as the amount of energy to be dissipated increases.

In US. Patent 2,901,710 to E. Garthwaite there is shown a load devicewhich includes an elongated resistor as the inner conductor and a pairof convergent plates disposed at opposite sides of the resistor as theouter conductor structure. The convergent ends of the plates areconnected to one end of the resistor and means are provided for applyinghigh frequency energy to be dissipated between the other end of theresistor and the divergent ends of the plates. The plates are verticallypositioned for excellent natural convection cooling of the load. Forgood matching of the load to the transmission line from the source ofenergy, the plates are substantially exponentially curved. With anexponential curvature of the plates, however, the plates are closelypositioned to the resistor at the rear end of the termination wherebyarcing may occur.

The principal object of the present invention is to overcome thisobjection by a simple configuration of outer conductor plates Withoutadversely affecting the matching of the load to the line.

This and other objects and advantages of the invention are achieved bythe provision of a slab line coaxial termination having an outerconductor structure which includes a pair of generally verticallypositioned convergent plates, which plates are curved inwardly at theupper and lower edges along a portion of the length thereof adjacent therear or convergent ends. The capacitance between the resistor positionedbetween the plates and the curved sections of the plates is increasedwhereby an increased spacing therebetween is permitted withoutdisruption of the impedance matching along the length of thetermination. The increased spacing decreases the possibility of arcingbetween the inner and outer conductor structures.

The invention may be fully understood from the following detaileddescription of the accompanying drawings. In the drawings, wherein likereference characters refer to the same parts in the several views:

FIGURE 1 is a diagrammatic top view of a termination embodying thisinvention;

FIGURE 2 is a side elevational view of the termination shown in FIGURE1, with parts shown broken away for clarity;

FIGURE 3 is a longitudinal cross-sectional view taken on line 3-3 ofFIGURE 1;

FIGURE 4 is a cross-sectional view taken on line 44 of FIGURE 2, and

FIGURE 5 is a development of the end portion of one of the outerconductors of the termination shown in FIG- URES 1 and 2.

Reference is first made to FIGURES 1 through 3 of the drawings whereinthe termination of my invention is shown comprising an elongated tubularfilm-type load resistor 10 disposed between a pair of convergent platesof identical construction but designated 11 and 11' for purposes ofidentification. Except for the inwardly curved end portions of theplates 11 and 11' which will be discussed infra, the plates aresubstantially plane so as to form a slab or strip line structure. Theconvergent ends of the plates 11 and 11' are connected to the rear endof the resistor 10 by means of a clamp 12. The resistor 10 comprises theinner conductor of the load and the plates 11 and 11' comprise the outerconductor structure thereof.

The divergent front ends of the plates 11 and 11 are secured by screwfastening means 13 to the vertical side walls of a front end connectorbody 14. A radially directed flange 16 is formed on the connector body14 by means of which the termination may be mounted on a suitablesupporting structure such as a housing or casing, not shown. A lineconnector member 17 threadedly engages a tapped through hole formed inthe connector body, and together with the connector body provides anelectrical connection between an attaching collar of a coaxial line, notshown, and the outer conductor structure 11, 11' of the termination. Atapered inner connector 18 is coaxially disposed with respect to themember 17 and is electrically insulated therefrom. The inner connector18 is conductively coupled to the front, or forward, end of theelongated resistor 10 and provides an electrical connection between aninner conductor of a coaxial line (not shown) attached thereto and theinner conductor 10.

As best seen in FIGURE 3, the tubular film-type load resistor 10 maycomprise a glazed cylindrical ceramic tube 24, with a resistive film 26disposed on the external surface thereof. Said film may comprise analloy including a highly stable tin oxide which is deposited on theexternal surface of the said glazed ceramic tube, which is then fired ata high temperature to disperse the resistance film throughout the bodyof the glaze. Bands 28 and 28' of conductive metal such as silver, areapplied to the ends of the resistor and extend over the resistance filmin good electrical contact therewith. It will here be understood thatfor purposes of illustration and clarity the showing of the resistancefilm 26 and conductive bands 23 and 28' are greatly exaggerateddimensionally in the drawing.

A generally cylindrical brass pin 29 conductively connects the taperedinner connector 18 to the forward end of the load resistor 10. Pin 29 isformed with integral axial flanges 31 and 32 at the opposite endsthereof. Flange 31 extends over the silver band 28 and is securedthereto by soldering or other suitable means, not shown. The flange 32extends over the inner free end of the connector 18 for good electricalconnection therewith. A dielectric bushing 33 is positioned in the spacebetween the pin 29 and connector body 14. 0 rings 34 and 36 positionedin grooves in the bushing provide fluid tight seals between the bushingand the connector body 14 and pin 29, respectively.

The flange 16 formed on the connector body 14 is provided with holes 38through which mounting bolts may extend for securing the termination toa suitable support or casing, not shown. As is well understood by thoseskilled in this art, terminations are commonly supported in casingscontaining a liquid dielectric such as transformer or mineral oil. Withthe outer conductor plates in a generally vertical position, thedielectric fluid easily circulates by convection past the load resistorfor cooling thereof, A flow of fluid through the tubular resistor ismade possible by radial holes 39 formed in the flange 31 of the pin 29.

The outer conductor plates 11, 11' are maintained a spaced distanceapart by dielectric spacers 21 made of polytetrafluoroethylene or thelike, secured to the plates by screw fastening means 22. For goodmatching of the termination to a coaxial transmission line the curvatureof the vertical outer conductor plates is substantially at anexponential rate. ture extended to the rear end of the plates, it willbe apparent that the plates would be closely positioned to the resistorthereat whereby arcing between the inner and outer conductors may occur.To prevent arcing, or to minimize the possibility of arcing, the rearend of the plates are altered in the manner of this invention (as shownin the drawings and described herein below) to provide a greater spacingbetween the plates and resistor atthe rear end of the termination thanis provided in prior art instructions, without an increased reactiveeffect manifested at the input to the load and without an increasedvoltage standing wave ratio thereat.

In accordance with my invention a novel outer conductor structure isprovided which both minimizes the voltage standing wave ratio in theline to the termination and provides for an increased spacing betweenthe inner resistor and outer conductor structure. As best seen inFIGURE4, each of the rear end portions 41 and 41' of the plates 11 and11' are inwardly curved to partially surround the resistor 10. As seenin FIGURES 1 and 4, the facing upper and lower edges of the inwardlycurved portions 41 and 41' do not meet but form continuous upper andlower gaps which permit an unimpeded thermosiphonic flow of coolingfluid over all portions of inner resistive rod 10 and which preserve theintegrity of the slab line structure 11-11. The rear end portions 41 and41' are also of a reduced height and are tapered toward the rear end ofthe termination. The upper and lower edges of the reduced height end arecurved inwardly to form the illustrated rear end portions 41 and 41.Reference is made to FIGURE 5 of the drawings wherein a development ofthe end section 41 of one of the plates 11 is shown. Notches 42, 42directed toward the center of the plate are formed between the mainvertical portion of the plate and the rear end portion 41, while similarnotches 43, 43 are formed between the rear end portion 41 and connectorend 44 to facilitate the curving of the plates therebetween. Holes 46are formed in the portions 41 and 41' for increased circulation of fluidpast the resistor.

By curving the outer conductor plates inwardly at the rear end thereofin the illustrated manner the capacitance between the inner and outerconductor structure is increased thereat whereby an increased spacingbetween the If, however, the exponential curvacurved section of theplates and the resistor may be employed for the proper impedancematching along this length or the termination. With an increasedspacing, the possibility of arcing is reduced.

My invention now having been described in detail in accordance with therequirements of the patent statutes, various changes and modificationswill suggest themselves to those skilled in this art, and it is intendedthat such changes and modifications shall fall within the spirit andscope of the invention as recited in the following claims.

I claim:

1. A microwave energy dissipating apparatus including an inner conductorcomprising an elongated resistor, an outer conductor structurecomprising a pair of continuous, convergent plates disposed at oppositesides of the resistor, means connecting theconvergent ends of the platesto one end of the resistor, said plates being substantially plane so asto form a slab line structure, the edge portions of said plates adjacentsaid convergent ends being inwardly curved so that the edges of one ofsaid end portions face the corresponding edges of the other of said endportions, said facing edges being spaced from each other to form twocontinuous gaps between corresponding edges of each of said endportions.

2. A microwave energy dissipating apparatus comprising an outerconductorstructure comprising a pair of generally vertically positionedconvergent plates, an elongated resistor positioned between the platesand connected at one end thereof to the convergent ends of the plates,an input conductor connected to the divergent ends of the plates and tothe other end of the resistor for connection of the apparatus to asource of microwave energy, said plates being substantially plane so asto form a slab line structure, the upper and lower edges of theconvergent end portions of said plates being curved inwardly so thatsaid edges face each other, said facing edges being spaced from eachother to form continuous upper and lower gaps between correspondingedges of said end portions to accommodate an unimpeded thermosiphonicflow of cooling fluid over all portions of said elongated resistor;

3. The invention as recited in claim 2 wherein said inwardly curved endportions of said plateshave vertical holes therethrough to accommodatean additional flow of cooling fluid.

References Cited by the Examiner UNITED STATES PATENTS I I 2,421,7586/47 Ovrebo 333-22 2,556,642 6/51 Bird 333-22 2,894,219 7/59 Frederico33322 2,901,710 8/59 Garthwaite 333-81 FOREIGN PATENTS 695,166 8/ 5 3Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

1. A MICROWAVE ENERGY DISSIPATING APPARATUS INCLUDING AN INNER CONDUCTORCOMPRISING AN ELONGATED RESISTOR, AN OUTER CONDUCTOR STRUCTURECOMPRISING A PAIR OF CONTINUOUS, CONVERGENT PLATES DISPOSED AT OPPOSITESIDES OF THE RESISTOR, MEANS CONNECTING THE CONVERGENT ENDS TO THEPLATES TO ONE END OF THE RESISTOR, SAID PLATES BEING SUBSTANTIALLY PLANESO AS TO FORM A SLAB LINE STRUCTURE, THE EDGE PORTIONS OF SAID PLATESADJACENT SAID CONVERGENT ENDS BEING INWARDLY CURVED SO THAT THE EDGES OFONE OF SAID END PORTIONS FACE THE CORRESPONDING EDGED OF THE OTHER OFSAID END PORTIONS, SAID FACING EDGES BEING SPACED FROM EACH OTHER TOFORM TWO CONTINUOUS GAPS BETWEEN CORRESPONDING EDGES OF EACH OF SAID ENDPORTIONS.